1. Field of the Invention
The invention relates to a turbine blade with a metal blade body and a protective coating constructed of a porous intermetallic felt, and in the blade body of the turbine blade cooling air channels are constructed that end at the intermetallic felt in order to supply it with cooling air.
2. Brief Description of the Related Art
DE 42 41 420 C1 describes a compressor blade consisting of a titanium alloy that is provided with an abrasive blade armor. The blade armor consists of a nickel matrix with enclosed boron nitride particles. This blade armor is provided preferably at the blade tip.
DE 32 03 869 A1 describes a turbine blade consisting of a basic body (core) of the metal turbine blade and a ceramic hollow body (blade shell). The blade shell is attached with metal retention pins to the turbine blade core. Insulation bodies inserted between the ceramic and metal contact surfaces are intended to reduce the heat flow from the blade shell to the turbine blade core.
DE 29 50 150 A1 introduces a sealing arrangement designed to seal a passage between a rotating and a non-rotating part. The sealing arrangement is provided with a surface seal and an edge part that is located opposite from the surface seal and is attached to the other part. The edge part has teeth that protrude into the surface seal that cut grooves into the surface seal when rotated, so that the seal arrangement forms a labyrinth seal.
The surface seal of this known seal arrangement is composed of metal fibers that form a mat-like or felt-like construction. This material is produced by sintering a matrix of randomly oriented metal fibers at a high temperature and reduced pressure, whereby a completely felted structure of metal fibers is formed which has metal bonds at all contact points of the fibers. The sintered material is characterized by an apparent density that is substantially lower than the density of the fibers themselves. The low density of the sintered fiber material is approximately in the range from 14 to 30%, and in this way these materials differ from sintered, pulverized materials with a density of more than 30%. This type of surface seal was used successfully because it has both the required strength, rigidity, and compactness and is also elastic, and can be comminuted and abraded.
GB 2 053 367 A describes a cooled gas turbine with a shield located opposite from the rotating blades. The shield is formed by a tubular ring with a rectangular cross-section which is able to hold cooling air in its interior. Holes have been provided in the ring wall opposite from the blades, and this wall is provided on the outside with a porous layer through which the cooling air is able to penetrate. The porous layer consists of a material sintered from small spheres. The spheres are constructed of a nickel-based super-alloy.
DE 2 038 047 describes a construction feature on guide vanes that is located inside the flow space of a steam turbine, in particular of saturated and wet steam turbines, and is used to drain water from the surfaces of the individual guide vanes. To reduce or completely prevent the erosion caused by water drop condensation on the surfaces of the turbine blades of wet steam turbines, the guide vane has drainage channels that are filled with porous, liquid-permeable material made from metallic materials or their alloys. The use of porous, liquid-permeable material has as its goal the specific drainage of water from the interior of a steam turbine.
DE 33 27 218 A1 describes a thermally highly stressed, cooled component, in particular a turbine blade, that is coated for reasons of reducing the heat stress with a metal felt layer that again is covered with an additional, ceramic heat insulation layer. In principle, the metal felt layer functions as an elastic carrier material for the ceramic heat insulation layer (see page 4, line 33 to page 5, 2; page 6, 1st paragraph and page 7, lines 2 to 7), but the metal felt layer also has a heat-dissipative action, especially since cooling air is supplied via cooling air grooves 3 (see FIG. 1) to the underside of the metal felt layer in order to cool it locally and in this way achieve an optimum heat dissipation of the heat flowing through the heat insulation layer 6.
With respect to the arrangement of the above quoted publication it can be said that metal felt is applied to the surface of turbine blades for thermal protection, but this protective effect is insufficient to protect the material from which the turbine blades are made from overheating, when the turbine blades encounter high thermal stresses.